Risk to Mogas availability?

[pmccarthy]

I went to fill jerry cans at my usual BP outlet today and the 95 pump was gone, replaced by a diesel pump. They said that demand for diesel is high and they had to recycle the pump space. If I want special petrol they still have 98. They said others are considering doing the same. I prefer 95 as it is more stable than 98 so will have to look further afield.

 

 

[turboplanner]

Some manufacturers have been shandying 95 with a significant amount of ethanol, so be very careful to check the product break down. This may have had more to do with the change, particularly in a rural area where petrol has to sit in tractor tanks, chainsaw tanks, stationary engine tanks for more than two weeks.

 

This is due to consumers pressurising the oil companies to supply cheaper petrol.

 

 

[bexrbetter]

I prefer 95 as it is more stable than 98 so will have to look further afield.

98 is of a slower and more consistent burning chemical makeup, so I don't understand why you think that.

 

98 offers better pinging and detonation resistance (won't add any power on a fixed ignition though) seems a no brainer to me if you can't get 95 on the day.

 

 

[facthunter]

Unless there is something known and specifically in 98, that causes fuel system components to deteriorate, I would always use it, The octane figures for Mogas and Avgas are NOT equivalent. 100 LL Avgas is way above 98 Mogas, so particularly with an aircooled motor, I would hesitate to risk using a lower octane that may have been shandied, more so than the Premium product would be likely to. Nev

 

 

[pylon500]

I prefer 95

Remember, when you look through the Rotax manuals for fuel type, it says 95 Minimum octane.

Higher is better, and as aimed at the performance car group, is less likely to be blended with ethanols etc.

 

But always ask at the counter, or read the bowser, they MUST state if any ethanol in the fuel.

 

 

[Yenn]

what is the definition of octane and does the number on the pump bear any relationship to real octane?

 

I wouldn't touch mogas for aircraft use except for Rotax and if I had a tank set aside touse mogas, so that it was not used at high power settings.

 

I have had detonation caused by poor fuel, when I couldn't get avgas.

 

 

[kgwilson]

My understanding is that the 98 octane Mogas blends have a significant quantity of aromatics, in them, one of these being toluene and these evaporate off first significantly degrading the fuel over time, more so than the BP 95 which I know a number of people have used for many years almost exclusively. I am not sure why BP, though some have said it definitely has no ethanol added. There were some very informative threads on this subject but I can't seem to locate them now.

 

 

[bexrbetter]

what is the definition of octane and does the number on the pump bear any relationship to real octane?

Octane is the rating of anti-volatility out of 100. Layman's terms; The higher the rating, the less chance of it being explosive.

 

Fuel does not "explode" in an engine, it burns rapidly and causes a rapid increase in pressure and that's what pushes your piston down the bore. Within the bounds of milli-seconds, it is actually a gradual and non-violent process. A sudden explosion, what you know as "detonation", simply damages things as explosions do.

 

Higher octane burns slower therefore has less chance of exploding therefore less chance of damaging stuff.

 

It is hard to accept for some people that the higher number means slower burning, people tend to equate that as meaning less power.

 

I wouldn't touch mogas for aircraft use except for Rotax and if I had a tank set aside touse mogas, so that it was not used at high power settings.

Octane rating that you can use is generally relevant to the compression ratio, ignition timing and combustion chamber shape.

 

Sometimes you can run a lower octane safely by simply retarding the ignition timing, other times it's more complicated. Rotax have a more modern combustion chamber shape than most, one of the reasons it's more tolerant. Most older aircraft engines have a terrible semi-hemi shaped chamber once thought to be the bee's knees. Jabiru chamber is very ordinary too.

 

 

[SDQDI]

My understanding is that the 98 octane Mogas blends have a significant quantity of aromatics, in them, one of these being toluene and these evaporate off first significantly degrading the fuel over time, more so than the BP 95 which I know a number of people have used for many years almost exclusively. I am not sure why BP, though some have said it definitely has no ethanol added. There were some very informative threads on this subject but I can't seem to locate them now.

That is also my experience. Our local servo used to stock ethanol free 95 and I used that without any hassles. Now though they have got rid of that and only stock 98, if used straight away or left in A sealed container no problem but I had it in the plane with no flying for just over two weeks and it had developed a horrible green gum in my fuel filters. I definately prefer the 95 but as it's not available 98 is my only option. (Just means I have to fly each week:wink: Not such a bad thing I guess.)

I've heard people say that 98 once the aromatics ect evaporate ends up back as 91 whereas the 95 seems more stable.

 

 

[turboplanner]

Now though they have got rid of that and only stock 98, if used straight away or left in A sealed container no problem but I had it in the plane with no flying for just over two weeks and it had developed a horrible green gum in my fuel filters.

It pays to get on the web and read the current specification sheets for that brand of fuel. The last time I checked, several companies were adding ethanol at differing amounts on differing octanes, so you can't be sure you're protected from gumming up just based on the octane figures.

 

I'm not saying your green gum was the result of ethanol, but if it was, you'll find it everywhere there was fuel, ie in the float bowls and lines, and in the very small air galleries.

 

I've heard people say that 98 once the aromatics ect evaporate ends up back as 91

I've heard that too on this forum. On the BP website they say that can happen with their 98, and spell out how that will affect your engine's operation, and recommend topping up with some fresh fuel to help that situation. I won't go into it here, because each application is different, but would recommend you read their website information, and if what they recommend sounds like a good idea for you to save wasting fuel, follow that up with a phone call to a BP technical person, telling them you are using it in an aircraft, just to make 100% sure.

 

 

[dazza 38]

My KTM's both run on Caltex 95. The fuel in the 640 Adventure can get up to a couple of months old as I ride my 1190 most of the time. I have never had a problem with old fuel and I don't add any additives. You blokes must be unlucky.

 

 

[facthunter]

Mogas degrades over a fairly short period. Generally there is no guarantee of it's consistency. All manner of tankers fill up other brands tanks. I've had less problems lately with cars than in the past. Running on gas and keeping at least 1/4 of a tank of petrol it gets pretty old, but no injector problems.

 

High octane resists ignition more. Doesn't self ignite when the engine is hot under load as much. On some motors cutting the ignition produces a running on situation if the motor is too hot. It is igniting itself without the spark happening. This is an uncontrolled ignition point and damaging to the motor. Nev

 

 

[dazza 38]

I keep hearing these stories of fuel degradation but I havent seen this from personal experience. My chainsaws can have six to 12 month old 2 stroke fuel in them and all I do is top the tank with fresh fuel without removing the old fuel even up the the ratio of 3/4 old fuel and 1/4 new fuel and they start no worries and run like a dream.

 

 

[turboplanner]

I keep hearing these stories of fuel degradation but I havent seen this from personal experience. My chainsaws can have six to 12 month old 2 stroke fuel in them and all I do is top the tank with fresh fuel without removing the old fuel even up the the ratio of 3/4 old fuel and 1/4 new fuel and they start no worries and run like a dream.

That's more or less what BP is saying, but anyone wanting to go down that path in an aircraft needs to get it direct frm BP, particularly the percentages.

 

 

[SDQDI]

I keep hearing these stories of fuel degradation but I havent seen this from personal experience. My chainsaws can have six to 12 month old 2 stroke fuel in them and all I do is top the tank with fresh fuel without removing the old fuel even up the the ratio of 3/4 old fuel and 1/4 new fuel and they start no worries and run like a dream.

But aren't you using 95?

I've never had a problem with 95 only with 98 if left too long and even then I never experienced any engine issues just the gummy residue. After removing the gummy residue I now use the plane each week and haven't had any issues since.

 

 

[dazza 38]

But aren't you using 95?I've never had a problem with 95 only with 98 if left too long and even then I never experienced any engine issues just the gummy residue. After removing the gummy residue I now use the plane each week and haven't had any issues since.

Yes 95

 

 

[K-man]

With the Rotax my first preference is 98 octane. I have no problem in using Avgas when Mogas is not available but have only rarely used 95 octane when the 98 was unavailable. I've never had a problem with any of it.

 

 

[turboplanner]

Yes 95

As I mentioned earlier it depends WHOSE 95.

Some have up to 15% ethanol, some have ethanol some of the time, and all are using it in the price war to keep the sale price per litre down, which is fine for cars but can be deadly for aircraft.

 

 

[K-man]

As I mentioned earlier it depends WHOSE 95.Some have up to 15% ethanol, some have ethanol some of the time, and all are using it in the price war to keep the sale price per litre down, which is fine for cars but can be deadly for aircraft.

I was under the impression that the amount of ethanol had to be advertised. A couple of years back we needed to top up our fuel at Drysdale River. We checked ahead of going there and they only had standard 91 octane and they weren't sure about ethanol. We then checked with the fuel distributor who informed us there was no ethanol in any of their fuel. (FWIW, we weren't flying on 91 octane, it was shandied 1:4 with Avgas.)

Normally we use Shell but sometimes Caltex. Other friends use BP. Obviously flying in the outback you don't have the luxury to choose, just to research beforehand.

 

 

[turboplanner]

I was under the impression that the amount of ethanol had to be advertised.

The Safeway service station I went into yesterday had replaced his 98 pumps with diesel in every lane (catering for the area), and there were no labels on the other pumps.

When I checked online afterwards, I found I'd filled with 10% ethanol in the 95 octane.

 

 

[facthunter]

Vev could answer a lot of these questions. He's involved in the industry.

 

Any one racing a two stroke seriously, wouldn't use stale fuel. I wouldn't fly a two stroke powered plane with stale fuel either. It goes absolutely rotten in some of the motor bikes I don't use regularly. Nev

 

 

[dazza 38]

I was under the impression that the amount of ethanol had to be advertised. A couple of years back we needed to top up our fuel at Drysdale River. We checked ahead of going there and they only had standard 91 octane and they weren't sure about ethanol. We then checked with the fuel distributor who informed us there was no ethanol in any of their fuel. (FWIW, we weren't flying on 91 octane, it was shandied 1:4 with Avgas.)Normally we use Shell but sometimes Caltex. Other friends use BP. Obviously flying in the outback you don't have the luxury to choose, just to research beforehand.

Yes, in QLD any fuel with ethanol in it must have a sign displayed on the bowser by law.

 

 

[turboplanner]

To a lot of them, laws are for other people Dazza, they don't want the sh!t, so what if someone's old Commodore or Victa won't start.

 

 

[dazza 38]

To a lot of them, laws are for other people Dazza, they don't want the sh!t, so what if someone's old Commodore or Victa won't start.

Yup so buy fuel from Caltex.

 

 

[Yenn]

What makes you think Caltex fyel is better. It is all up to the owner of the servo.